The capacities of batteries in battery-based uninterruptible power supplies (UPSs) vary depending on several factors, including temperature, age, and load. As the batteries age, they are preferably replaced once their capacities drop below desired capacities (e.g., runtimes). Preferably, the batteries are replaced before their diminished capacities affect desired operation of the UPSs, e.g., by relying on a battery with an undesirably-low runtime such that the UPS is unable to provide backup power to a load for a desired amount of time. To determine when a battery's capacity has diminished more than desired before being relied on to power a load, periodic testing may be performed on the battery.
Previously, determining a UPS's battery capacity has involved powering a load with the battery to fully discharge the battery to determine the battery's capacity. This can take a long time (e.g., 20 hours) and when the battery is significantly or completely depleted, the UPS cannot provide desired/adequate backup power.